AHA: Guidelines Not a Factor in Warfarin Choices

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Explain that a review of warfarin prescriptions for patients with atrial fibrillation revealed no correlation with CHADS2 scores or a history of stroke despite guideline recommendations.

Note that the study was based on two national ambulatory care surveys of 23 million office visits from 2005-2007.

CHICAGO -- Clinicians do not seem to be relying on the recommended stroke risk score to prescribe warfarin for patients with atrial fibrillation, researchers found.

In an analysis of a national database of outpatient visits, the use of warfarin in patients with atrial fibrillation did not correlate with the CHADS2 score (OR for high-risk versus lower risk patients 1.19, 95% CI 0.85 to 1.67), according to Geoffrey Barnes, MD, of the University of Michigan in Ann Arbor.

A history of stroke was not significantly related to warfarin use either (OR 1.31, 95% CI 0.83 to 2.07), he reported at the American Heart Association meeting here.

The findings indicate that clinicians are not following guidelines from the American College of Cardiology and the AHA, which recommend using the CHADS2 score to guide antithrombotic therapy, Barnes said. The score is calculated by giving one point each for heart failure, hypertension, age 75 or older, and diabetes, and two points for a history of stroke, for a maximum score of 6. Scores of 2 and above indicate high risk.

"So I think it really raises the question as to why and what can we do to increase education and also to give better tools that practitioners feel like they can use to appropriately treat patients," Barnes said.

To look at warfarin use nationwide, he and his colleagues analyzed data on outpatient visits for patients with atrial fibrillation from the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey. They looked at 23 million office visits from 2005 to 2007.

Over the three-year period, there was little variation according to CHADS2 score in the rate of warfarin use; 55.3% of patients with a score of 0 -- in whom the bleeding risk of warfarin would likely outweigh any benefit -- received the drug. Only 58.3% of the patients most likely to benefit -- those with scores of 2 to 6 -- received warfarin.

"So there seems to be a little bit of a disconnect" between CHADS2 score and the use of warfarin, said Barnes, who speculated that risk of bleeding, which is hard to quantify, may be causing clinicians to shy away from giving the drug to everyone who needs it.

He said that highlights the need for a standard tool to assess bleeding risk.

"We use a very scientific tool to predict stroke but we just kind of eyeball it for bleeding," according to Barnes.

Ralph Sacco, MD, a neurologist at the University of Miami in Florida and president of the AHA, told MedPage Today that the reason for the lack of good correlation between CHADS2 score and warfarin use and the slow acceptance of the guidelines is hard to understand.

He said that bleeding is the top concern among clinicians when considering warfarin for their patients, but that other subjective factors enter into the decision-making process, including an assessment of unstable gait and cognitive problems, as well as a patient's unwillingness to take a drug that carries a risk.

When asked if more educational outreach is needed to get clinicians to embrace the CHADS2 score for deciding when to use warfarin, Sacco suggested that the newer anticoagulants -- referring to the direct factor Xa inhibitors -- might make its use less important.

"What these new drugs that are coming on the market obviously do is they open up the potential use of drugs that may be safer, don't require blood testing, and may have less drug-drug interactions and food interactions," Sacco said. "So the safety profile in the newer drugs may be the best thing for stroke prevention in atrial fibrillation."

However, he said, the use of the CHADS2 score should not be abandoned.

"Yes, we should still be educating physicians about the CHADS2 score, because even with these new drugs, the CHADS2 score will be helpful in selecting patients for certain treatments for atrial fibrillation."

Barnes reported that he had no conflicts of interest. His co-authors reported relationships with CVR Global, the Michigan Department of Community Health, Blue Cross Blue Shield of Michigan, the NIH, Mardigian Foundation, Fibromuscular Disease Society of America, Pfizer, sanofi-aventis, and Merck/Schering-Plough.

Sacco served on the data safety and monitoring committee for AVERROES, a trial of the investigational direct factor Xa inhibitor, apixaban.

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